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Pre tensioning system
Post tensioning system
The various types of devices used for tensioning steel
are grouped under four principal catagories.
◦ Electrical or Thermal
Mechanical devices Hydraulic devices
It includes weights with or
without lever transmission.
Geared transmission in
conjunction with pulley
Screw jacks with or without
In simple it is wire binding
Hydraulic jacks are the
simplest means of producing
large prestressed forces or
extensively used as tensioning
This systems are used for the
ranges of 5 to 100tonnes
Large hydraulic jacks for
forces in the range of 200 to
600tonnes have also been
developed by baur-leonhardt.
Electrical or Thermal devices Chemical devices
It have been used
successfully in 1958 for
tensioning of steel wires and
The steel wires are
electrically heated and
anchored before placing of
concrete in the moulds.
It is also called as thermo-
Expanding cements are used
and the degree of expansion
is controlled by varying
Since the expansive action
of cement by sitting in
restrained it induce tensile
forces in tendon and
compressive forces in
Freyssinet anchorage system
Gifford Udall systems
Magnel blaton system
Baur Leonhardt system
This system is widely used in Europe and India
It consists of a cylinder with a conical interior through
which the high tensile wires pass and against the walls
of which the wedged by a conical plug lined
longitudinally with grooves to house the wires.
The main advantage of this system is that a large
number of wires or strands can be simultaneously
tensioned using double acting hydraulic jacks.
It is developed in UK.
It consists of steel split cone and cylindrical female
cone anchorages to house the high tensile wires bearing
against steel plates.
Each wire is tensioned separately and anchored by
forcing a sleeve wedge into a cylindrical grip resting
against a bearing plate.
The ducts are generally formed by metal sheaths cast
into the concrete member.
In this method, the tendons comprise high tensile bars
of diameter varying from 12 to 40mm which are
threaded at the ends.
After tensioning, each bar is anchored by screwing a
nut and washer tightly against the end plates.
In this system the forces are transmitted by the bearing
at the end blocks.
While the system eliminates the loss of stress due to
anchorage slip, it has a disadvantage in that curved
tendons cannot be used.
This system adopts metallic sandwich plates, flat
wedges, and a distribution plate for anchoring the
Each sandwich plate can house up to four pairs of
The distribution plate may be cast into the member at
the desired location.
The number of wires in the magnel cable varies from 2
This system is well suited for transmitting large forces.
A BBRV tendon consists of several parallel lengths of
high tensile wires, with each end terminating in cold
formed button head with a machined anchorage fixture.
In the case of tendons formed by strands, they are
anchored to the machined fixture by split cone sleeves.